Method of making through-connections by controlled punctures



H" C. SCHEQK Um 17 WW! METHOD OF MAKING THROUGH-CONNECTIONS BY CONTROLLED PUNCTURES 2 Sheets-Sheet 1 Filed June 16, 1965 INVEHTOR C. SONIC HENPY ATTORNEY UM, 117, fi fi' c, sc c 3,346,95Q

METHOD OF MAKING THROUGH-CONNECTIONS BY CONTROLLED PUNCTURES Filed June 16, 1965 2 Sheets-5heet 2 BRUSH PLATING EQUIPMENT United States Patent Ofitice 3,346,95d Patented Get. 17, 1967 3,346,950 METHOD 6F MAKING THRUUGH-CUNNEC- TIONS BY C(PNTROLLED PUNCTURES Henry C. Schick, Hopewell Junction, N.Y., assignor to international Business Machines Corporation, Armonk,

N .Y., a corporation of New York Filed .liune 1d, 1965, Ser. No. 464,467 3 Claims. (Cl. 29-625) ABSTRACT F THE DISCLOSURE A method and associated means are disclosed for establishing small area through connections, between conductors disposed on opposite faces of an insulator. At desired points of interconnection a small area of a conductive line element on one surface of an insulator body is depressed into and through the adjacent insulator material into contact with a point on a conductor on the opposite surface of the insulator body. The opposite conductor is backed by a supporting plate or the equivalent to arrest the movement of the depressing tool at its inner surface. The de pressing tool is shaped to exert a stressing force on the depressed conductor to a point beyond the elastic limit of its constituent material such that worked material of this conductor is capable of withstanding the tendency of the displaced insulator material to relax into its former position after removal of the depressing tool. The connection thus formed may be electrically and structurally reinforced by plating additional conductive matter into the depressions utilizing the undeformed conductors as receiving electrodes of a plating system.

This invention pertains to the extension of electrical connections through insulator bodies by a method which is simpler, more reliable, and more convenient for miniaturized circuit applications than previous methods.

In the art of extending electrical connections through insulator bodies, there has arisen a need for improved methods adaptable for use in increasingly concentrated miniaturized circuit applications. Methods known to be presently in use involve either the formation of conductive links via holes extending completely through the insulator body or the application of heat to deform the insulator body at selected regions whereby conductors on opposite surfaces may be crimped or welded together in such regions. These methods are more complicated, require more skill to practice, and require larger contact or land regions on the insulator body surface than the presently contemplated method.

A primary object of this invention, therefore, is to provide a method for extending electrical connections through insulator bodies which is distinguished by its relative simplicity, reliability, and adaptablity to miniaturized circuit applications.

Another object is to provide an improved method and apparatus for forming electrical through-connections in an insulator body which can be readily incorporated into a small portable kit and used by field maintenance personnel with little training.

A feature of the invention involves the use of a controlled piercing technique to form openings or depressions extending through conductors on one face of an insulator body and terminating at, but not penetrating, conductors on an opposite face of the same body. These openings are so formed that the insulator material displaced by the puncturing instrument is not fractured and yet cannot relax to its original position upon removal of the instrument to isolate the unpenetrated conductors from the opening. Thus the connections may be secured merely by filling the openings with conductive matter. This is preferably and most conveniently accomplished by a plating process as described herein.

These and other objects and features of this invention will become apparent upon consideration of the follow ing description given With reference to the accompanying drawings wherein: 7

FIG. 1 is an elevational view of a segment of a circuit member having relatively isolated patterns of conductive lines disposed on opposite faces of its insulator body;

FIG. 2 is a sectional view of the member of FIG. 1 taken along lines 22 shown in FIG. 1;

FIGS. 3-6 are sectional views corresponding to that in FIG. 2, taken at various stages of the application of the process of this invention to the member, as an electrical connection is being established between conductors disposed on opposite faces of the insulator body of the member;

FIG. 7 illustrates a field connection kit for making rapid connections FIG. 8 is a view in elevation of a portion of an insulator member carrying predetermined patterns of unconnected conductive lines on its opposite surfaces which can be variably inter-connected in a simple manner by means of the present invention;

FIGS. 9 to 11 inclusive are views in section of the member shown in FIG. 8 during various steps in the process of forming through and cross-over connections between conductors on the strip;

FIG. 12 is a view in elevation of the same member upon completion of the connection formations.

Referring to FIGS. 1 and 2, a segment of a circuit member, upon which the method of the present invention may be practiced, is illustrated therein. This member includes conductors 1 and 2 which are adhered to opposite faces of the insulator body 3 of the member. As shown in FIGS. 3-6 the present invention is practiced by controllably piercing an opening extending through a portion of the thickness of the member defined by the two conductors and the thickness of the insulator body. The depression thus formed extends through one of the conductors, conductor 1 in this instance, and terminates at but does not penetrate the other conductor, conductor 2 in this instance. In one specific application of the invention restrained punctures are made, after first cleansing the surfaces of the members to remove oxide accumulations from the conductors such as l, which are to be pierced, by rigidly supporting the conductors such as 2, which are not to be penetrated, against a hard backing surface; for example, against the flat surface of a glass backing plate such as 4 (FIG. 3). The unsupported conductor such as 1 is pierced with a sharp puncturing instrument or tool 5, wielded with moderate pressure. After passing through the conductor ll, the point of the tool 5 continues to penetrate through the insulator body 3 until it is restrained by the inner surface of the rigidly backed conductor 2 where considerably more pressure would be required to continue the movement of the tool. The object at this point is to remove the tool 5 and establish a secure electrical connection between conductors 1 and 2 through the opening 6 remaining after removal of the tool.

This is possible only if certain restrictions are observed. First, the material of the insulator body 3 must not be permitted by virtue of its elasticity to flow back into the region of the opening 6 after removal of the tool, since the conductors l and 2 would then be again electrically isolated from each other by solid matter, and second, the material of the body 3 and conductor 2 must not be subjected to splitting or shearing stresses of such magnitude as to weaken, crack, or excessively deform the material of the member outside of the pierced regions such as 6.

One way of preventing elastic relaxation of insulator material into the region 6 after removal of the tool 5 is suggested in FIGS. 3 and 4. As shown therein the tool 5 is so dimensioned that it bends the soft copper of conductor 1 beyond its elastic limit forcing it to line the walls of the cavity region 6 in a relatively fixed position, thereby preventing movement of the insulator back into the region 6. Such formations have been satisfactorily produced by a tool which tapers to a point at a 30 angle (this bends the cavity-lining conductor such as 1 through an angle of approximately 75) on members composed of polyethylene terephthalate insulator bodies .004 inch thick to which are adhered .001 inch thicknesses of copper conductor arranged in line patterns in which the line width is nowhere greater than .001 inch. Under such conditions secure through-connections have been established directly between point contact regions of the conductors without build-up of land area extension around the contact regions.

Alternative choices of material to prevent recovery of the insulator material into the opening left by the piercing tool or of constraints to control the travel of the piercing tool will readily suggest themselves to those skilled in the art. For example, penetration of the tool may be resisted by permanently adhering a layer of insulative backing material to the surface of the member on which the conductors such as 2 are disposed. For best results the piercing tool should not be manipulated directly by hand, but should be guided and controlled by precisely positioned mechanical members.

It should also be understood by those skilled in the material working arts that there is a limit to the shape and volume of material which can be displaced by piercing or coining in the manner suggested in FIG. 3, beyond which cracks or deformities 7 (FIG. 4A) would be produced in the insulator body external to the displacement region 6. Constraints must therefore be placed on one or more of the following parameters: the thicknesses of the regions to be pierced, the shape of the piercing tool in the region of its piercing end, the elasticity of the materials used in the conductive line patterns and insulator body, and the amount of outcropping or deformation of the insulator body which will be considered tolerable. In connection with the last-mentioned factor it should be observed that if circuit members are to be stacked vertically to produce multiple layered packages, a minimum amount of outcropping or deformation in each layer would be considered tolerable, whereas a member not confined to a restricted region of space in the direction of its thickness could tolerate considerably more displacement or deformation in that direction, subject, however, to the restriction that cracks or faults must not be produced in the body of the member.

Assuming that precautions are observed as outlined above, the cross-sectional appearance of the member after removal of the piercing tool will correspond to the formation shown in FIG. 4. The pierced conductor such as 1 will contact the unpenetrated conductor such as 2 in a more or less secure mechanical and electrical connection. The connection is subsequently reinforced mechanically and electrically by depositing additional conductive matter into the depression 6, preferably by plating since depressions such as 6 which are imperfectly formed due to undertravel of the piercing tool or to elastic recovery of the displaced insulator would then fail to receive a build-up of plate metal and could be detected by visual inspection.

Apparatu for brush plating, which can be used without extensive training by field maintenance personnel is suggested in FIG. 5, although for mass production of through connections more sophisticated apparatus would be preferred. As shown in FIG. 5, the unpierced face of the member is held in contact with a conductive plate such as 8 through which the conductors such as 2 make contact with negative terminal 9 of D.C. power source 10. The positive terminal 11 of this source is connected to a plating electrode 12 which is immersed in a plating solution held in a container 13. One end of this container contains ducts communicating with brush 14, so that when the brush is passed across the pierced face of the member plating metal 15 passes out of solution and collects primarily in the cavity regions such as 6. A switch 16 is provided for controlling the flow of plating current.

In more sophisticated mass-production apparatus for use under controlled laboratory conditions, the openings such as 6 would be formed by automatically operated and controlled mechanisms and after all openings had been formed, the pierced members would be immersed in a plating bath with the unperforated conductors such as 2 coupled to one electrode of a plating system and the cavity openings such as 6 exposed to the opposite electrode disposed within the bath. A predetermined amount of plating current would then be supplied for a predetermined time to deposit the desired thickness of plate material into the cavities.

In plating into .005 inch deep openings 6 in polyethylene terephthalate members, satisfactory plates have been obtained under laboratory controlled conditions in which the pierced members are immersed in a weak acid aqueous solution of metallic salt, the metal constituent of which is gold, copper, cadmium, or the like, and are subjected to a plating current of 10 amperes for intervals ranging between 20 and 30' seconds per application. Such plating solutions and selective plating apparatus suitable for the applications thereof are extensively available commercially from plating equipment manufacturers such as Selectrons Limited of New York, NY. A typical solution found to yield satisfactory results is composed of a suspension of gold in a weak acid maintained at 0.7 to 1.5 troy ounces of gold per gallon of liquid with a pH maintained between 4.2 and 4.5 and with conductive salts added to maintain a specific gravity of 1416 Baum.

Following the application of the plating material, the member may be inspected either visually through magni fying optics, or electrically, to determine whether all desired connections have been established. An electrical test set-up is shown in FIG. -6. The conductors such as 2 are coupled to one terminal of a D.C. source 17, the opposite polarity terminal of which is connected through a probe and indicating device 18 to perforated conductors such as 1. Failure of the plate to take in any cavity region such as 6 is accompanied by an open circuit indication. If only a few out of many punctures in a member are found to be faulty it is a simple matter to re-puncture these few and re-plate selectively, only over the repunctured regions, using the brush plating apparatus of FIG. 5. If all punctures in an entire member were found to be electrically open after plating, it would be immediately apparent that either the travel of the punctur ing tool had been overly restricted or that the member undergoing processing was defective in some dimension or material of its composition.

It has been noted that even some poorly prepared members may take to plating. This has been verified by experiments in which control punctures were made using pressure calculated to barely leave the inner surfaces of the backed conductors exposed for plating. Yet it was found that a substantial proportion of such marginal formations could be effectively converted into complete connections by plating with the current specified above.

While it is considered most advantageous from an inspection and reliability viewpoint to use the plating procedure just described for reinforcing punched connections, it should be understood that the last step of the inventive process can in some instances be suitably carried out by other means, for example, by spraying a suspension of metal through a mask. The effects of the latter method, however, would not be subject to immediate visual inspection as with plating.

While it is probably most useful to employ a tool having a conically shaped piercing end, it is not absolutely necessary to do so. A wedge-shaped tool, for example, could be used to cut completely through the line such as 1 leaving a wedge-shaped depression in the region 6. Then, however, the conductor such as 1 would not completely line the walls of the region and the probability of elastic recovery of the insulator into the region 6 would consequently be increased.

Proceeding now with the description of a portable kit assembly for making printed wiring connections in the field, an exemplary arrangement is shown in FIG. 7. This includes a supply of prefabricated polyethylene terephthalate insulator sheets 19, in rectangular 9 inch by 13 inch segments, each having pre-existing matrix patterns of thin conductive lines 20 and 21 adhered to opposite faces thereof. It should be observed that the sheets are devoid of extended conductive land areas both prior to and after the formation of through connections in the manner described below with reference to FIGS. 8 to 12.

In an exemplary application contemplated for the sheets 19, a variable network of eletcrical connections is produced by forming connections between intersecting point regions of the lines. For this application the lines 26) on one face of the sheet extend parallel to each other in a first direction and the lines 21 on the opposite face also extend parallel to each other but in a second direction different from the first one, the conductors 2t} and 21 thereby forming a matrix of over-lapping point regions 22, at which through-connections may be formed.

The field kit further includes a glass back-up plate 23, a punching tool 24, a cleaning brush 25, a supply of cleansing soap powder 26, a scraping knife 27, for removing sections of pre-existing conductive lines, and portable brush plating equipment 28. The plating equipment includes a power supply 29, cathode 30, and a plating anode chamber 31 terminating in brush fibers 32. Portable plating equipment of this type is commercially sold by the aforementioned Selectrons Limited as Economy Model 220 SB, and by Brooktronic Engineering Corp. of North Hollywood, Calif, under the product designation Portable Plater.

As shown by way of example in FIGS. 8 to 12, through and cross-over connections may be formed using the kit assembly of FIG. 7 on flat strips or sheets 37. The sheet 37 in the specific application shown in FIGS. 8 to 12 is a rectangular sheet, 9 inches by 13 inches, having pre-existing diagonally oriented conductive line patterns on opposite faces thereof. In this application the lines were intended to carry data signals characterized by frequencies of such magnitude that signal delays through connecting circuits such as those to be formed in the sheet 37, represent significant design factors. To maintain uniform signal delays, therefore, it is desirable to arrange the pre-existing copper line patterns to provide a long basic or nominal delay between opposite edges of the sheet, whereby departures from the basic delay, due to through and crossover connections, would be proportionately lessened in relation to the basic delay. Hence, the lines on the sheet 37 are shown, in FIG. 8, in what is considered the preferable diagonal orientation, the parallel lines 38 on the upper face of the sheet forming oblique angles with the edges of the sheet, and the parallel lines 39 on the lower face of the sheet (shown in broken outline in FIG. 8) extending in a direction perpendicular to the'lines 38.

By way of example, it is desired to form one connection between segments 40A and 41B of respective conductors 40 and 41 on the upper face of the sheet 37, and another connection between segments 40B and 41A of the same conductors which is electrically isolated from the firstmentioned connection. In preparation for this, the face of the sheet containing these conductors is thoroughly cleansed, and then discontinuities and through-connections are formed at selected positions along in the conductors 40 and 41, and the intermediate conductor 42. As shown in FIGS. 9 to 12, discontinuities are formed by scraping away portion of the conductors at, for example, region 43 of the conductor 40, regions 44 and 45 of conductor 42, and region 46 of conductor 41. Also shown in the same figures are the connection perforations, 47 and 48 in conductor 40, 49 and 50 in conductor 42, and 51 and 52in conductor 41.

As shown in FIGS. 9 to 11, the perforations are formed with the sheet 37 held against a glass backing plate 53. The segments 40B and 40A (FIG. 9) isolated from each other by discontinuity 43, are respectively connected to over-lapped regions of conductors 56 and 57 on the underface of the sheet 37. The strap-like segment 58 of conductor 42 (FIG. 11), isolated from the rest of conductor 42 by discontinuities 44 and 45, provides a bridging connection, between conductors 57 and 59 on the underface, via the perforations 49 and 50. Finally, the segments 41A and 41B (FIG. 10) isolated from each other by discontinuity 46 are respectively joined to underface conductors 56 and 59, via perforations 51 and 52. Thus, after plating over the cavities 47 to 52 there is an electrical connection (FIG. 12) extending from segment 40A to segment 41B, via plated-over perforation 47, conductor 57, plated-over perforation 49, strap 58, plated-over perforation 50, conductor 59, and plated-over perforation 52. Similarly, there is seen to be a connection between segments 40B and 41A, via plated-over perforation 48, conductor 56, and plated-over perforation 51.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that changes in form and details may be made therein without departing from the spirit and scope of the invention as characterized in the following claims.

What is claimed is:

1. A method of forming an electrical connection between a pair of conductive lines adhered to opposite faces of an insulator body comprising:

cleaning one face of said member to remove oxide film accumulations from the outer surfaces of conductive lines adhered thereto, including one line of said pair of lines;

controllably piercing an opening extending through one line of said pair and said insulator body and terminating at but not penetrating the other conductive line of said pair; employing a perforating instrument dimensioned to cause deformation of the material of said one line in the pierced region beyond the elastic limit of said material thereby deforming said line to form a retaining wall in said opening which will tend to retain its shape upon removal of the instrument; and

depositing additional conductive matter into said opening to provide a permanent electrical connection between said pair of lines;

wherein said step of depositing is accomplished by an electroplating process in which the said other conductive line of said pair is connected to one terminal of a source of direct current and the opening region retained by the one line of said pair is controllably exposed through an electroplating solution to an electrode of an electroplating system including said source and said other line.

2. A method of selectively forming multiple throughconnections between patterns of conductive lines adhered to opposite faces of an insulator body comprising the steps of:

cleaning the outer surfaces of the conductive lines adhered to one face of said insulator body to prepare said lines for connection to conductors on the other face;

backing the conductive lines on the other face of said insulator body against a rigid support member; piercing a plurality of openings extending through selected positions of lines on said one face and terminating at but not penetrating lines on said other 7 8 face, using a perforating tool dimensioned to cause of permanent or at least semi-permanent contact deformation of the conductive matter of the pierced with opposite interior points of conductive segments through lines in the pierced region beyond the elastic on said opposite face; limit of said matter; and utilizing one or more of said line segments on said electroplating additional conductive matter into all of 5 opposite face as a deposition electrode of a brush type said openings simultaneously electroplating system, brushing said line segments on 3. A method of producing small area through connecsaid one face with the brush electrode of said elections between thin conductive line segments carried on troplating system thereby plating additional conducopposite faces of an insulator substrate which method is tive material into one or more of said depressions in sufficiently simple to be performed in a field location 10 one operation. utilizing only a small complement of portable and relatively inexpensive apparatus, said through connections References Cited being narrower than the respective line segments linked UNITED STATES PATENTS thereby, said method comprising steps of:

cleansing the outer surfaces of all line segments on one 15 4/1961 Telfer 174-6185 X face of Said Substrate 55,809 11/1964 Griswold 17468.5 X 3 264 402 8/1966 Shaheen et a1. 17468.5 holding the opposite face of said substrate and the line iegments thereon in intimate contact with a con- OTHER REFERENCES orming surface of a relatively inflexible supporting Structure; 20 New Advances In Printed Circuits, U.S. Dept. of forming depressions at selected points in said line seg- InmerCe, National Bureau of Standards, Miscellaneous ments on said one face extending said segments into Publication Published 1948 PP- 48 and and completely through the intervening insulator material of said substrate into an unyielding position DARRELL CLAY Primary Exammer' 

1. A METHOD OF FORMING AN ELECTRICAL CONNECTION BETWEEN A PAIR OF CONDUCTIVE LINES ADHERED TO OPPOSITE FACES OF AN INSULATOR BODY COMPRISING: CLEANING ONE FACE OF SAID MEMBER TO REMOVE OXIDE FILM ACCUMULATIONS FROM THE OUTER SURFACES OF CONDUCTIVE LINES ADHERED THERETO, INCLUDING ONE LINE OF SAID PAIR OF LINES; CONTROLLABLY PIERCING AN OPENING EXTENDING THROUGH ONE LINE OF SAID PAIR AND SAID INSULATOR BODY AND TERMINATING AT BUT NOT PENETRATING THE OTHER CONDUCTIVE LINE OF SAID PAIR; EMPLOYING A PERFORATING INSTRUMENT DIMENSIONED TO CAUSE DEFORMATION OF THE MATERIAL OF SAID ONE LINE IN THE PIERCED REGION BEYOND THE ELASTIC LIMIT OF SAID MATERIAL THEREBY DEFORMING SAID LINE TO FORM A RETAINING WALL IN SAID OPENING WHICH WILL TEND TO RETAIN ITS SHAPE UPON REMOVAL OF THE INSTRUMENT; AND DEPOSITING ADDITIONAL CONDUCTIVE MATTER INTO SAID OPENING TO PROVIDE A PERMANENT ELECTRICAL CONNECTION BETWEEN SAID PAIR OF LINES; WHEREIN SAID STEP OF DEPOSITING IS ACCOMPLISHED BY AN ELECTROPLATING PROCESS IN WHICH THE SAID OTHER CONDUCTIVE LINE OF SAID PAIR IS CONNECTED TO ONE TERMINAL OF A SOURCE OF DIRECT CURRENT AND THE OPENING REGION RETAINED BY THE ONE LINE OF SAID PAIR IS CONTROLLABLY EXPOSED THROUGH AN ELECTROPLATING SOLUTION TO AN ELECTRODE OF AN ELECTROPLATING SYSTEM INCLUDING SAID SOURCE AND SAID OTHER LINE. 